Fuel tanks may include a fuel supply line for supplying fuel to an engine, and a fuel return line for returning unused fuel from the engine to the fuel tank. The fuel supply line and the fuel return line may each include a shutoff valve therein to prevent fuel flow when shutoff is desired. For safety reasons it may be desirable that the shutoff valve for the supply line and the shutoff valve for the return line both be closed or both be open and that a one-open/one-closed condition be avoided.